metamorphic
Gossan (with secondary copper minerals)
Iron-rich oxidized rock cap (Limonite/Goethite with Malachite/Chrysocolla inclusions)
Hardness: 4-6 (variable); Color: Rusty yellow-orange to brown with greenish-blue staining; Luster: Dull, earthy; Crystal Structure: Amorphous/massive; Specific Gravity: 3.3-4.3
- Hardness
- 4-6 (variable)
- Color
- Rusty yellow-orange to brown with greenish-blue staining
- Luster
- Dull, earthy
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Physical properties
Hardness: 4-6 (variable); Color: Rusty yellow-orange to brown with greenish-blue staining; Luster: Dull, earthy; Crystal Structure: Amorphous/massive; Specific Gravity: 3.3-4.3
Formation & geological history
Formed by the intense oxidation and weathering of primary sulfide ore deposits (like pyrite or chalcopyrite). Rainwater reacts with minerals to leach out sulfur and create sulfuric acid, leaving behind iron oxides and secondary carbonates/silicates.
Uses & applications
Used historically by prospectors as an indicator of underlying metal ore deposits (gold, copper, silver). Sometimes collected as decorative garden stone or 'ore indicators'.
Geological facts
Gossans are known as 'iron hats' and were once the primary way miners located deep copper and gold veins before modern geophysical imaging was available.
Field identification & locations
Look for heavy, porous rocks with intense rust staining and bright green or blue streaks in mining districts. Often found near fault zones or volcanic-hosted deposit sites.
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